Method of producing electronics substrate with enhanced direct bonded metal

ABSTRACT

A substrate for electronic components is formed by bonding a cooling metal layer to one side of a ceramic tile and bonding an electronic metal layer to the other side of the electronic tile. The substrate is secured to a machining base and the cooling metal layer surface is enhanced through an MDT process. In the process, fins are sliced into the cooling metal layer with a tool to a depth of less than the cooling metal layer thickness. The slicing forces material upward without removing material from the cooling metal layer, forming fins that extend beyond the original thickness of the cooling metal layer. The fins can be cross-sliced at an angle to form pins.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/191,281 filed on Jul. 26, 2011 which claims the benefit of U.S.Provisional Patent Application 61/368,475, filed Jul. 28, 2010. Theentire contents of U.S. application Ser. No. 13/191,281 filed on Jul.26, 2011 are herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to electronic substrates with direct bonded ordirect plated metals, where the surface of the direct bonded or directplated metal is enhanced for heat transfer purposes.

Description of the Related Art

Certain electronic devices generate heat as they operate, and in somecases this heat has to be removed or dissipated for the device tocontinue operating properly. Several techniques have been used to coolelectronic equipment. Examples include fans, which are used to blow airover electronic equipment. This air serves to convectively cool theelectronic equipment with normal ambient air. Other techniques that havebeen used include liquid cold plates. Liquid cold plates are plates withchannels through which liquid flows. The electronic equipment is mountedin contact with a liquid cold plate and the heat generated by theelectronic equipment is transferred to the liquid coolant inside theplate. This can provide better cooling than the convective coolingprovided by a fan with considerably less flow volume. It can alsoprovide better temperature consistency with less acoustic noise.

Cold plates can be directly affixed to a heat-producing piece ofelectronic equipment, such as an electronic chip or an insulated gatedbipolar transistor (IGBT). It is also possible to use thermal grease orother heat transfer aid between the electronic equipment and the coldplate to improve heat transfer. Typically, the cold plate includes aninlet and an outlet for liquid coolant flow. The liquid coolant absorbsthe heat produced by the electronic equipment, and transfers theabsorbed heat to the coolant which then flows out of the cold plate.Many cold plates provide cooling with a relatively low flow of liquidcoolant. They can provide better temperature consistency than convectivecooling, minimal acoustic noise and the cooling power of liquidcoolants.

Several factors impact the performance and desirability of cold plates,and different factors are important for different uses. Some importantfactors include cost of production and ease of producing relativelylarge quantities. Cooling efficiency should be high, and cold platesshould be securely sealed to prevent any leak of liquid coolant onto theelectronic equipment being cooled.

In some applications, the coolant may not be particularly clean, whichcan result in plugging of the cold plate. For example, a cold plate usedin an automobile may utilize the anti-freeze liquid for cooling, and theanti-freeze can contain small particulates. In other applications, theremay be a phase transfer within a cold plate to help facilitate cooling.It is also possible for a cold plate to be used for heating a componentby replacing the coolant with a heating fluid. One primary differencebetween a coolant and a heating fluid in one phase heat transfer is thatthe temperature of a coolant is lower than the item being cooled, andthe temperature of a heating fluid is higher than the item being cooled.

Many different techniques are used to cool electronic components, andnew techniques which provide cooling benefits are desirable.

BRIEF SUMMARY OF THE INVENTION

A substrate for electronic components includes a ceramic tile and acooling metal layer. The cooling metal layer can include copper,aluminum, nickel, gold, or other metals. The cooling metal layer has anenhanced surface facing away from the ceramic tile, where the enhancedsurface includes either fins or pins. Electronic components can beconnected to the substrate on a surface opposite the cooling metallayer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a schematic diagram of one embodiment of a cooling system.

FIG. 2 depicts a side view of one embodiment of a substrate with anelectronic component mounted on the substrate.

FIG. 3 is an exploded, perspective view of one embodiment of a substratewith mounted electronic components and a heat exchange device.

FIG. 4 is a cross-sectional side view of one embodiment of a substratewith mounted electronic components and heat exchange devices.

FIG. 5 is a side view of one embodiment of a tool forming fins from asubstrate.

FIG. 6 is a perspective view of one embodiment of a tool forming finsfrom a substrate.

DETAILED DESCRIPTION Heat Transfer Fundamentals

There are several ways to cool electronic equipment. Often times,electronic equipment is cooled with fans which blow air over theelectronic equipment. This air provides convective cooling which doeshelp to control the heat generated by the electronic equipment. However,liquid cooling can provide greater cooling capacity than air flow inmany situations.

Liquids can provide better cooling than gases for several reasons. Forexample, liquids are denser than gases so more thermal mass is availableto absorb heat from the electronic equipment. Also, liquids generallyhave higher thermal conductivities so heat will transfer into andthrough the liquid more rapidly than heat will transfer into and througha gas. Furthermore, liquids tend to have a higher specific heat thangases so a set quantity of liquid will absorb and transfer more heatthan a comparable amount of gas. Because of this, when electronicequipment is utilized which produces large amounts of heat, manymanufacturers desire the use of liquid cooling devices.

Liquid cooling systems include at least a liquid coolant and an articleor substance that is cooled. Often, there is a barrier between theliquid coolant and the item being cooled, and heat must be transferredthrough this barrier. In some instances, the barrier can includemultiple components and layers. A barrier between the item being cooledand the liquid coolant is generally desired for electronic equipment,because direct contact with liquids can damage some electroniccomponents. Minimizing the resistance to heat flow through the barrierbetween the item being cooled and the liquid coolant improves thecooling efficiency.

Two significant forms of resistance to heat flow through a barrierinclude resistance through one material, and resistance across aninterface between two separate components or parts. Resistance to heatflow through a single material is minimized if the material is a heatconductor, instead of a heat insulator. Copper is one material that canbe used in a barrier, because it is a good conductor of heat and it isrelatively malleable. However, other materials can also be used,including aluminum, steel and other metals, graphite, ceramics, and eveninsulating materials like plastic or air.

Another source of resistance to heat flow is at the interface betweentwo components or parts. Typically, when heat flows from a firstcomponent to another component which contacts the first, there is aresistance to heat flow between the two components. Reducing the numberof interfaces can improve heat transfer rates. Also, when two materialsform an interface, there can be air trapped between the two materials,and air is an insulator that tends to hinder heat transfer. Thermalgrease can be used to facilitate heat transfer between two differentcomponents or layers in a barrier, but a single heat transfer layer istypically more efficient than two separate layers even when thermalgrease or other heat transfer agents are used.

It is also desirable to maximize the surface area where the coolingliquid contacts the barrier because the larger the surface area, themore area available to transfer heat. The use of fins, pins, or otherstructures on a surface contacting the liquid coolant can increase thesurface area and improve heat transfer. Surface area can be furtherincreased by increasing the number of fins, pins, or other structures,or by increasing the surface area of each fin, pin, or structure. Asurface with fins, pins, or other structures to improve heat transfer issaid to be “enhanced,” so the fins, pins, or other structures can begenerically referred to as enhancements.

Forming enhancements directly from a heat transfer surface, instead ofattaching the enhancements to the heat transfer surface, can improveheat transfer because this eliminates the interface between the base ofthe heat transfer surface and the enhancement. Therefore, by formingfins or other enhancements from the material of the heat transfersurface, resistance to heat flow is minimized. If one were to producethe enhancements separately and then affix them to the heat transfersurface, there would be a resistance to heat flow between theenhancements and the heat transfer surface at the interface, which wouldhave a negative impact on the heat transfer rate. This is true even ifseparate enhancements and the heat transfer surface were made from thesame material, such as copper. Therefore, it is preferred to form theenhancements directly from the material of the heat transfer surfacesuch that the enhancements are an extension of the heat transfersurface, and there is no interface between the enhancements and heattransfer surface. This is referred to as having the enhancements“monolithic” with the heat transfer surface.

In some cases, liquids will flow across a solid in what is referred toas laminar flow. In laminar flow, the layer of liquid directlycontacting the solid surface remains essentially stationary at the solidsurface. The layer of liquid directly above that layer moves verygradually across the first layer. The next layer up moves a little moreswiftly, etc., such that the highest flow rate will be at a pointrelatively far from the solid surface. The lowest flow rate, which isessentially zero, will be at the solid surface. Each different layer ofliquid which is sliding over the adjacent layers provides its ownresistance to heat flow, and each layer can have a different temperatureso the warmest liquid is often adjacent the solid surface and thecoolest liquid is relatively far from the solid surface. Therefore, ifthe liquid can be mixed during flow, the liquid directly contacting thesolid surface can absorb heat from the solid surface and then be mixedwith the entire body of cooling liquid to spread the absorbed heat intothe liquid more rapidly.

Turbulent flow causes liquids to mix as they flow across a solidsurface, as opposed to laminar flow. This tends to keep the liquid incontact with the solid surface cooler, which facilitates a fastertransfer of heat from the solid surface to the liquid. Some things whichtend to increase turbulent flow include faster flow rates, unevensurfaces, projections into a flowing liquid, and various obstructionsthat force a liquid to change path and flow another way. To maximizeturbulence, one can include sharp bends, twisting edges, pins, fins, andany of a wide variety of flow obstructions that cause rapid change inthe direction of flow of a liquid. Many structures which increaseturbulence can also increase pressure drop across a cold plate.Increased pressure drop can lower the flow rate, so a balance must beobserved to ensure efficient heat transfer. Obstructions which tend toincrease the amount of fluid flow close to the solid surface also tendsto increase heat transfer, because this reduces the thickness of anystagnant liquid layer at the solid liquid interface, and it also reducesthe distance heated liquid has to travel to intermix with the main bodyof cooling liquid.

In some embodiments, the liquid can be boiled, or vaporized, in the heattransfer process. This is referred to as two phase cooling because thecoolant changes phase from a liquid to a gas in the cooling process. Aliquid absorbs heat to vaporize, so the heat of vaporization of theliquid is absorbed, and this can increase the overall cooling effect.This description explains one phase cooling only, but it is to beunderstood that two phase cooling could also be used and is included asan embodiment of this description. Two phase cooling can require someadditional components, such as a condenser to re-liquefy the coolantfrom a gas, as is understood by those skilled in the art. The principlesdiscussed in this description also apply to two phase cooling.

In many electronic cooling systems, the coolant is recirculated and usedrepeatedly. In the embodiment shown in FIG. 1, a fan 2 is used to blowcooling air through a convective cooling device 4, and the coolant ispumped through the convective cooling device 4 by a pump 6. The coolantexiting the convective cooling device 4 is relatively cool, and ispumped through a heat transfer device 10 which is connected to anelectronic component 8. The coolant is heated as the electroniccomponent 8 is cooled, and the heated coolant is then pumped back to theconvective cooling device 4 to be cooled once again.

There are many possible variations to this cooling system. For example,the coolant can be used to cool many different electronic components 8before returning to the convective cooling device 4, and these differentelectronic components 8 can be connected in series, parallel, or both.The convective cooling device 4 can be replaced with a heat exchangerthat cools the coolant with another liquid, such as once through coolingwater. The cooling system can use once through cooling liquid, and it iseven possible for the system to be used for heating components insteadof cooling them because the same heat transfer principles apply toheating as to cooling.

Electronic Substrates

Many electronic components 8 are assembled on an electronics substrate12, as shown in FIG. 2. The substrate 12 can provide interconnectionsnecessary to form an electric circuit, similar to a printed circuitboard. The substrate 12 can also be used to help cool the connectedelectronic components 8. One type of substrate 12 used is a directbonded copper (DBC) substrate 12, where a layer of copper is directlybonded or directly plated to one or both sides of an insulatingmaterial, such as a ceramic tile 14. It may be possible to use otherelectrically insulating but thermally conductive materials in place ofthe ceramic tile 14, such as different polymers, foams, or otherelectrical insulators. A direct plated copper substrate 12 can also beused for electric circuits, where direct plating is an alternativemethod of fixing metal to a substrate 12. In this description, the term“direct bonded copper” and “DBC” are defined to include direct bondedcopper and direct plated copper. Similarly, it is to be understood thatreferences to direct bonded aluminum or other direct bonded metals alsoinclude direct plating of the metal to the substrate 12.

In some embodiments, the copper layer on one side is pre-formed oretched to form at least part of the electrical circuit, and the copperlayer essentially covers the other side to help spread and transfer heatto cool the electrical components. In alternate embodiments, aluminumcan be directly bonded or directly plated to a ceramic tile 14 insteadof copper. It is even possible to use other metals or other materials inplace of the copper or aluminum.

These directly bonded or directly plated metallic layers are referred toin this description as the cooling metal layer 16, and the electronicmetal layer 18. In general, the electronic metal layer 18 can bepre-formed or etched for the electrical circuit, and the cooling metallayer 16 can be used for thermal management, but it is possible thatneither metal layer 16, 18 forms part of the circuit, or both metallayers 16, 18 form part of electrical circuits. The ceramic tile 14 hasan electronics face 17 opposite a cooling face 15, and the cooling metallayer 16 is directly bonded to the cooling face 15 while the electronicmetal layer 18 is directly bonded to the electronic face 17.

The ceramic tile 14 can be formed from aluminum oxide (Al₂O₃), aluminumnitride (AlN), beryllium oxide (BeO), or other materials, and frequentlyhas a thickness between about 0.28 millimeters (mm) and 0.61 mm, butother thicknesses are possible. The cooling and electronic metal layers16, 18 can be a wide variety of materials, and the thickness of themetal layers 16, 18 can depend on the metal used, desired performance,and other factors. A copper layer directly bonded or directly plated tothe ceramic tile 14 frequently has thicknesses ranging from 0.25 mm to0.41 mm, but other thicknesses are possible. When an aluminum layer isdirectly bonded or directly plated to the ceramic tile 14, the thicknessof the aluminum layer can be approximately 0.3 mm, but other thicknessesare possible. In one embodiment, the cooling metal layer 14 has acooling metal layer thickness 19 which can be between 0.2 and 0.5millimeters.

In some embodiments, the cooling layer outer surface 20 and/or theelectronic layer outer surface 22 can have a first coating layer 24, thefirst coating layer 24 can have a second coating layer 26, and there canbe additional coating layers as well. The cooling and electronic layerouter surfaces 20, 22 are the surfaces facing away from the ceramic tile14. The “cooling layer outer surface 20” is defined to mean the coolingmetal layer 16 outer surface before any fins or other enhancements areformed from the cooling metal layer 16, or a section of the coolingmetal layer 16 which has not had any fins or enhancements formed fromit. The electronic layer outer surface 22 is similarly defined, exceptwith reference to the electronic metal layer 18 instead of the coolingmetal layer 16. The first coating layer 24 can be low phosphoruselectroless or electrolytic nickel, and the second coating layer 26 canbe a gold layer, but other material combinations are possible. Thenickel layer can be about 2 to 7 micrometers (um) thick, and the goldlayer can be about 80 nanometers (nm) thick, but other thicknesses foreach layer are also possible. It is also possible to directly bond acopper layer to one side of a ceramic tile 14, and an aluminum layer tothe other side of the ceramic tile 14, or to use other combinations ofmetals for the cooling and electronic metal layer 16, 18.

The direct bonded or direct plated copper substrates 12 tend to have arelatively low coefficient of thermal expansion that is close to thecoefficient of thermal expansion of silicon, due to the high bondstrength of copper to the ceramic substrate 12. Many electroniccomponents 8 contain silicon, so having a substrate 12 with a similarcoefficient of thermal expansion can increase thermal cyclingperformance. The fact that the direct bonded or direct plated coppersubstrate 12 has a coefficient of thermal expansion similar to that ofsilicon can also reduce the need for interface layers between thesubstrate 12 and silicon components. The direct bonded or direct platedcopper substrates 12 have many desirable characteristics known to thoseskilled in the art, including good heat spreading and thermalconductivity, as well as a high electrical insulation value.

Connecting the direct bonded or direct plated copper, or the directbonded or direct plated aluminum substrates 12 to a cold plate or othercoolant containing device can provide for liquid cooling. In oneembodiment, heat has to transfer from the electronic component 8 to theelectronic metal layer 18, then to the ceramic tile 14, then to thecooling metal layer 16, then to the wall of the cold plate, and thenfinally to the cooling liquid. There may also be thermal grease betweenthe cooling metal layer 16 and the wall of the cold plate. Providing anenhanced surface on the cooling metal layer 16, and moving coolantdirectly past the enhanced cooling metal layer 16 would reduce theresistance to heat transfer created by the interface between thesubstrate 12 and the cold plate, and also the resistance to heattransfer through the barrier wall of the cold plate.

Heat Exchange Device on Electronic Substrates

A heat exchange device 10 can be affixed to the substrate 12 for thermalmanagement, as seen in FIGS. 3 and 4 with continuing reference to FIGS.1 and 2. The heat exchange device 10 can comprise a tub 28 that isaffixed to the substrate 12 to create a chamber 30 adjacent to thesubstrate 12. Alternatively, the chamber 30 can be made with a spacerand a cover, or many other structures which provide an enclosed spaceadjacent to the substrate 12. An inlet 32 and an outlet 34 are provided,where the inlet 32 and outlet 34 penetrate the chamber 30 to allowliquid to flow into and out of the chamber 30, so the inlet 32 andoutlet 34 are in fluid communication through the chamber 30. The inlet32 and outlet 34 can penetrate the tub 28, but it is also possible forone or more of the inlet 32 and outlet 34 to penetrate the substrate 12to provide access to the chamber 30, or to penetrate any other structureused to make the chamber 30. There can be more than one inlet 32 andoutlet 34, as desired, and a nozzle 33 can be used at the inlet 32and/or outlet 34 to facilitate connections to fluid handling systems orto direct fluid flow in the chamber 30.

The tub 28 can be affixed to the cooling metal layer 16 such that thecooling metal layer 16 forms a part of the chamber 30, so fluid flowingthrough the chamber 30 would contact and pass directly over the coolingmetal layer 16. The cooling metal layer 16 can be machined to form anenhanced surface 35, where the enhanced surface 35 comprises fins 36,but it is also possible for the enhanced surface 35 to comprise pins 38or other structures, as desired. In general, the tub 28 is connected tothe cooling metal layer 16 such that the enhanced surface 35 ispositioned within the chamber 30, so coolant will contact and flowdirectly past the enhanced surface 35. In some embodiments, noenhancements are made to selected portions of the cooling metal layer16, so this unenhanced portion of the cooling metal layer 16 can be usedto form a seal with the tub 28, which can help prevent coolant leaks.The chamber 30 maintains liquid coolant over the enhanced surface 35,but the chamber 30 also serves to contain the liquid coolant and therebyprotect the electronic components 8, the electronic metal layer 18, andother components from direct contact with the liquid coolant. Thechamber 30 is one portion of a liquid coolant containment system.

Enhancements primarily include fins 36 and pins 38 of various shapes anddimensions, but can also include other structures like hollow verticalcircular protrusions, horizontal hollow boxes, or other shapes. Pins 38include rectangular or round fingers extending from the cooling layerouter surface 20, but pins also include other shapes like pyramids orsemi spheres. The enhancements can extend from the substrate 12 all theway to the tub 28, so the enhancements actually touch the inner surfaceof the tub 28, or the enhancements can extend to a distance short of thetub inner surface. Enhancements which touch the tub 28 can result inhigher heat transfer rates than shorter enhancements, but they can alsoresult in higher pressure drops which may lead to lower coolant flowrates, and lower coolant flow rates can decrease heat transfer rates.The shape and size of the enhancements can also affect the pressure dropand heat transfer rates.

The fins 36 provide increased surface area for heat transfer, and alsocan increase turbulence in the coolant flow, both of which can increaseheat transfer rates. Channels 44 are positioned between adjacent fins36, and fluid can flow through the channels 44, as seen in FIGS. 5 and6, with continuing reference to FIGS. 1-4. Fluid flowing through thechannels 44 is in close proximity to the fins 36, and heat transferbetween the fluid and the fins 36 can be rapid. Fins 36 have been usedfor some time to increase heat transfer, and the size, shape, andstructure of the fin 36 can all impact the overall heat transfer rate. Awide variety of fin sizes, shapes and structures can be used on thecooling metal layer 16. Fin structures can include such things asplatforms at the top of a fin 36, crenellated fin tops, sideprojections, etc. Pins 38 provide similar heat transfer improvements forsimilar reasons, and can also include structural modifications orenhancements.

The tub 28 or other structures forming part of the chamber 30 can beover essentially all of the cooling metal layer 16, but in otherembodiments the chamber 30 will cover only a portion of the coolingmetal layer 16, or there may be a plurality of different chambers 30covering various different portions of the cooling metal layer 16. Thesize and spacing of the enhancements can vary between different chambers30, and even within one chamber, as desired. There can be a plurality ofenhanced surfaces 35 on one cooling metal layer 16, and each differentenhanced surface 35 can comprise the same type of enhancement ordifferent types of enhancements. The plurality of different enhancedsurfaces 35 on a single cooling metal layer 16 can be discrete, separate“islands,” within discrete, separate chambers 30. In alternateembodiments, the different enhanced surfaces 35 can be within the samechamber 30, where the different enhanced surfaces 35 can be connected,or the different enhanced surfaces 35 can be separated by a portion ofthe cooling metal layer 16 which is not enhanced. The tub 28 or otherstructures can be connected to the substrate 12 in a wide variety ofmethods, including but not limited to soldering, screws, pins, adhesive,and sonic welding. The connection between the components that form thechamber 30 should be secure to prevent coolant leaks.

Providing a chamber 30 with coolant flow directly contacting the coolingmetal layer 16 at the enhanced surface 35 can improve heat transferrates by reducing the number of interfaces and layers between anelectronic component 8 and the coolant, as discussed above.Additionally, providing a thin substrate 12 with a directly connectedcooling chamber 30 can reduce the space required for electroniccomponents 8 for several reasons. First, a thin substrate 12 requiresless room than a thicker substrate 12. Secondly, a cooling chamber 30directly connected to the substrate 12 can reduce the total amount ofmaterial between the electronic component 8 and the coolant, and lessmaterial takes up less space. Thirdly, the use of liquid coolant canprovide increased cooling over convective cooling with air flow, soelectronic components 8 may be positioned closer together while stillmaintaining thermal control.

Surface Enhancements

The substrate 12 includes a ceramic tile 14 and a cooling metal layer16, and machining can be used to enhance the cooling metal layer 16 toform an enhanced surface 35. The ceramic tile 14 is a brittle material,so any machining done to the substrate 12 should prevent flexing orbending of the substrate 12, and should also control other stresses thatcan fracture or break the ceramic tile 14. Generally, when one side ofthe substrate 12 is being machined, the entire opposite side should befirmly supported so all forces applied can be transferred straightthrough the substrate 12 directly to the supporting surface. Whilemachining, the substrate 12 should be secured to prevent slipping orother motion. In one embodiment, the substrate 12 is flat, so thesupporting surface should also be flat for machining. Additionally, themachining operation should be very precise, because all the variouscomponents of the substrate 12 can be thin, so there is little marginfor error.

The substrate 12 can be secured to a machining base 50 by severaltechniques known to those skilled in the art. Some techniques forsecuring the substrate to the machining base 50 include securing a stopblock 52 to the machining base 50, and abutting the substrate 12 againstthe stop block 52 such that the stop block 52 prevents the substrate 12from slipping as the tool 40 passes through the cooling metal layer 16.Screws 54 can secure the stop block 52 to the machining base 50, butclamps, bolts, welding, or many other techniques can also be used. Thesubstrate 12 can be further secured to the machining base 50 withclamps, but vacuum applied to the substrate surface contacting themachining base 50 can secure the substrate 12 in place withoutobstructing the substrate surface being machined.

The current invention includes a method of enhancing the cooling layerouter surface 20, and also a method for enhancing the electronic layerouter surface 22 if desired. The electronic layer outer surface 22 canbe enhanced in the same manner as the cooling layer outer surface 20, sothis description will only describe enhancing the cooling layer outersurface 20 with the understanding that the electronic layer outersurface 22 could be enhanced in the same manner.

Fins 36 can be formed on the cooling metal layer 16 using a processcalled micro deformation technology (MDT), which is described in U.S.Pat. No. 5,775,187, issued Jul. 7, 1998, and which is herebyincorporated in full into this description. In this process, the coolingmetal layer 16 is sliced with a tool 40 without removing material fromthe cooling metal layer 16. The MDT) process is different than a saw orrouter, which removes material as cuts are made, and is more similar tothe cutting of meat with a knife.

The slicing of the cooling metal layer 16 is done with the tool 40. Asthe tool 40 contacts the material of the cooling metal layer 16, a fin36 is cut into the cooling metal layer 16. The slicing of the fins 36from the cooling metal layer 16 results in the fins 36 being monolithicwith the cooling metal layer 16, which improves heat transfer asdiscussed above. The fins 36 are formed directly from the material ofthe cooling metal layer 16, so there is no joint or break between thefin 36 and the cooling metal layer 16.

The fins 36 are one embodiment of an enhanced surface 35. The cutting ofthe cooling metal layer 16 forms a channel 44 between adjacent fins 36,and can be done without removing material from the cooling metal layer16. Preferably, there are no shavings produced in the formation of thefins 36. The tool 40 cuts fins 36 into the cooling metal layer 16, andthe space produced as the tool 40 passes through the cooling metal layer16 forces material in the fins 36 upwards. This cutting and deformationof the cooling metal layer 16 causes the fins 36 to rise to a fin height46 which is higher than the original cooling layer outer surface 20. Thecutting tool design, the depth of the cut, and the width of the fins 36and channels 44 are factors which affect the fin height 46. The tool 40is moved slightly in one direction for each successive cut, so each cutforms a fin 36 adjacent to the previously cut fin 36. This process isrepeated until a bed of fins 36 has been produced.

Pins 38 are made by slicing across the fins 36 with a second series ofcuts. The second set of slices can also use the MDT method, and raisethe pins 38 to a pin height 48 greater than the fin height 46. As theslices are made, no material is removed from the cooling metal layer 16,so the moved material is instead directed into the remaining pin 38.This causes the remaining pin 38 to rise to a height higher than thematerial from which the pin 38 was cut. The second set of slices can bemade at a wide variety of angles to the fins 36, including ninetydegrees or an angle other than ninety degrees. Additionally, the inclineangle of the pin 38 and/or the fin 36 can be manipulated by the angle ofthe tool 40 as the slices are made. A modification of the incline angleof the fin 36 can change the incline angle of the pin 38.

In an alternate embodiment, the fins 36 are made without using the MDTprocess, and the pins 38 are then formed from the fins 36 using the MDTprocess. In another alternate embodiment, the fins 36 are made using theMDT process, and the pins 38 are then formed from the fins 36 using aconventional cutting process different than the MDT process.

The fins 36 are cut at a specified fin width 37, with a specifiedchannel width 45, so there are a predetermined number of fins 36 percentimeter. Similar specific dimensions can be set for pins 38. Manydimensions of the enhanced surface 35 can be controlled by specifyingthe tool design and settings for the machining operation used. Theproduction of the tub 28 or comparable structures can be accomplished bytraditional methods. This includes stamping, cutting, pouring, molding,machining and other standard metal working techniques.

The MDT cutting process can be performed on a CNC milling machine, alathe, a shaper, or other machining tools. The cutting depth should notbe so deep that the integrity of the ceramic tile 14 is compromised, andthe cutting depth should be deep enough to produce a fin height 46sufficient to achieve the desired heat transfer rate. Experience hasshown a cutting depth of about 60 to 70 percent of the cooling metallayer thickness 19 can be used. In general, the tool 40 should cut intothe cooling metal layer 16 to a depth less than the cooling metal layerthickness 19. Successful beds of fins 36 have been made with betweenabout 20 to about 60 fins per centimeter (cm), but other fin densitiesare also possible. One example of fin dimensions on direct bondedsubstrates includes a cooling metal layer thickness 19, as measuredbefore the fins 36 are cut, of 0.30 mm, and a fin height 46 of 0.53 mm,a fin width of 0.17 mm, and a channel width of 0.17 mm. As describedabove, the cooling layer outer surface 20 is determined either beforethe fins 36 are cut or at a point where no fins 36 are formed in thecooling metal layer 16. The fin height 46 is larger than the coolingmetal layer thickness 19, and the fins 36 begin at a point within thecooling metal layer 16, so the fins 36 extend beyond the cooling layerouter surface 20. As described above, the pins 38 extend to a pin height48 which is higher than the fin height 46 before the pins 38 were made.Therefore, the pins 38 extend beyond the cooling layer outer surface 20,similar to the fins 36.

In one embodiment, a lathe is used for machining blank substrates 12,where a substrate 12 is considered blank before the cooling metal layer16 is enhanced. The lathe can have a disk-shaped face that isperpendicular to the axis of rotation, and one or more blank substrates12 can be secured close to the outer edge of the face of a lathe. Theblank substrates 12 can be set opposite each other to help balance thelathe face during rotation. The tool 40 can then be directed into theface of the lathe, essentially parallel to the axis of rotation of thelathe, for machining of the substrates 12. The tool 40 is slowly movedeither towards the axis of rotation of the lathe, or away from the axisof rotation of the lathe, so the tool 40 contacts the blank substrates12 at different positions with every rotation of the lathe. In thismanner, several blank substrates 12 can be machined simultaneously on asingle lathe. Machining near the edge of the face of lathe produces fins36 which are not straight, but which have a slight curve determined bythe distance of the substrate 12 from the lathe's axis of rotation.Border areas can then be machined flat for mounting a tub 28 sealed tothe cooling metal layer 16, if desired.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed here.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. A method of producing an electronics substrate comprising: directly bonding a cooling metal layer to a first side of a ceramic tile, the ceramic tile comprising a thickness of between 0.28 mm and 0.61 mm, the cooling metal layer having a thickness of between 0.25 mm and 0.41 mm, and; directly bonding an electronic metal layer to a second side of a ceramic tile; securing the ceramic tile to a machining base such that the electronic metal layer is firmly supported; slicing fins into the cooling metal layer with a tool to form an enhanced surface, where the tool slices into the cooling metal layer to a depth less than the cooling metal layer thickness, and where the slicing step forces sliced material upwards without removing material from the cooling metal layer.
 2. The method of claim 1, wherein the tool slices into the cooling metal layer to a depth of less than 70 percent of the cooling metal layer thickness.
 3. The method of claim 1 further comprising: connecting a tub to the cooling metal layer such that a chamber is formed between the tub and the cooling metal layer, and where the enhanced surface is positioned in the chamber; and forming a coolant inlet and a coolant outlet that penetrate the chamber.
 4. The method of claim 1 further comprising: connecting a plurality of electronic components to the electronic metal layer.
 5. The method of claim 1 where the step of cutting fins into the cooling metal layer further comprises forming the fins to a fin height extending beyond an outer surface of the cooling metal layer.
 6. The method of claim 1 further comprising slicing across the fins at an angle to form pins which extend beyond an outer surface of the cooling metal layer.
 7. The method of claim 6, wherein the angle is between 30 and 90 degrees.
 8. The method of claim 1 where the ceramic tile consists of aluminum oxide, aluminum nitride, beryllium oxide, or any combination thereof. 